Exercise by itself won’t help you lose weight.
This is not to say that exercise isn’t good for you; it is, in fact, great for you. It conveys an astonishing array of health benefits.
But — and we all hate hearing this — many experts, while extolling the benefits of exercise, say the primary villain when it comes to excess weight is what’s on our menu. To lose weight, we have to cut calories.
Exercise helps keep lost pounds off, but exercise alone can’t do the initial job of losing it.
“I think the role of exercise in weight loss is highly overrated,” says Marc Reitman, chief of the diabetes, endocrinology and obesity branch of the National Institute of Diabetes and Digestive and Kidney Diseases, or NIDDK. “I think it’s really great for being healthy, but I’m a strong believer that overeating is what causes obesity. To exercise your way out of overeating is impossible.”
Michael Joyner, a Mayo Clinic researcher who studies how people respond to the stress of exercise, agrees. “The key for weight loss is to generate and maintain a calorie deficit,” he says. “It’s pretty easy to get people to eat 1,000 calories less per day, but to get them to do 1,000 calories per day of exercise — walking 10 miles — is daunting at many levels, including time and motivation,” he says.
To be sure, some people can work weight off, experts say. These include those who exercise vigorously for long periods, and professional athletes, who typically engage in high-intensity workouts.
But they are the exceptions. Those high-level workouts are “not something most people do,” says Philip F. Smith, co-director of NIDDK’s office of obesity research. “Walking for an hour won’t do it.”
Joyner agrees. “Theoretically, people can exercise enough to lose without changing what they eat, but they have to exercise a whole lot,” he says.
Moreover, moderate exercise doesn’t really burn all that many calories, especially when you think about a single piece of chocolate cake, which has between 200 and 500 calories. Most people burn only about 100 calories for every mile of running or walking, although this can vary depending on the person, according to Joyner. Put another way, to lose one pound, you must run a deficit of about 3,500 calories — meaning that if you burn an excess 500 calories a day, it would take a week to drop that pound.
Kevin D. Hall, an NIDDK scientist who studies how metabolism and the brain adapt to diet and exercise,…